CO₂ methanation over Ni/SiO₂–Al₂O₃ catalysts: effect of Ba, La, and Ce addition

One of the most technologically and financially feasible methods for managing anthropogenic CO₂ emissions is CO₂ hydrogenation to methane. However, the high efficiency of mostly used nickel-based catalysts is still a challenge in the CO₂ methanation process. Herein, 10% silica-90% alumina, commercially known as SIRAL-10, was used as a support for nanostructured Ni catalysts. Modified SIRAL-supported nickel catalysts (Ni/SA) with Ba, La, and Ce metals as promoters were prepared by a simple wet impregnation method. These catalysts were tested for atmospheric CO₂ methanation reaction in a 250-500 °C temperature range in a tubular fixed bed reactor with a H₂/CO₂ molar ratio of 4. As prepared samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, hydrogen temperature-programmed reduction (H₂-TPR), carbon dioxide temperature-programmed desorption (CO₂-TPD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). CO₂ methanation was found to be highly dependent on surface basic sites and Ni dispersion. Ni active sites were mainly obtained from the reduction of strongly interacted NiO at temperatures >700 °C. All promoted catalysts showed better catalytic activity than unpromoted nickel catalysts. Maximum CO₂ conversion of 85.6% was obtained on the Ba-promoted sample at 400 °C, while low-temperature catalyst activity was achieved in the case of Ce-Ni/SA. The catalysts exhibited CH₄ selectivity in the following order: Ce-Ni/SA > Ba-Ni/SA > La-Ni/SA > Ni/SA. The Ce-containing sample showed exceptional catalytic performance with about 78.4% CO₂ conversion and 98% CH₄ selectivity at 350 °C. Both Ba and Ce-promoted catalysts exposed the best stability for 24 hours. Unique features of the SIRAL support and the addition of basic promoters facilitated the sequential hydrogenation of CO₂ to produce almost CO-free CH₄.